#include <stdio.h>

#define exchange(a,b)
{\
    //宏定义中允许包含两道衣裳的情景，此时必须在最右边加上"\"
    int t;\
    t = a;\
    a = b;\
    b = t;\
}

void main(void)
{
    int x = 10;
    int y = 20;
    printf("x = %d; y = %d\n",x,y);
    exchange(x,y);
    printf("x = %d; y = %d\n",x,y);
}